The current version of internet protocol, IPv4 (Internet Protocol version 4), is running out of address space to deploy new addresses. A new version, IPv6, has been developed with a much larger address space and is in the early phase of deployment. During this period of utilization of IPv4 and IPv6, one method of achieving deployment has been to run “Dual-stack,” an approach featuring a node having both an IPv4 and an IPv6 address. This approach allows a node to reach IPv4-only destinations, but ultimately does not save any IPv4 address space. Alternatively, use of non-unique private IPv4 addresses (also called RFC 1918 (Request for Comment) addresses) along with public IPv6 addresses has been developed, but such an approach may require a standard IPv4 NAT (Network Address Translation) in the network along with all the usual methods for distributing and managing those private addresses at the hosts.
Another approach, called “Dual-stack lite” or “DS-lite” has been developed and standardized in RFC 6333 (http://tools.ietf.org/html/rfc6333 on May 24, 2012). For DS-Lite, the host uses an IPv6 transport to reach an AFTR (Address Family Translator), which connects to IPv4 addresses (and potentially also acts as a NAT). The Address Family Translator may be an independent device but may also function within a network device (e.g. a router) already deployed in the network. When a DS-lite encapsulated packet reaches the AFTR, it removes the encapsulation and forwards the internal packet after performing any network address translation required.